P0646: Air Conditioning Clutch Relay Control Circuit Low
What to do
Driveable. If the air conditioning seems to be running even when switched off, or the engine feels down on power with poor economy, that is the likely explanation.
What this code means
The air conditioning clutch relay circuit is reading low — a short to ground, or a relay stuck closed. A compressor engaged continuously is worth catching: it loads the engine at all times, hurts economy, and can freeze the evaporator.
Likely causes
Start here
- Failed air conditioning clutch relay · easy
- Signal wire shorted to ground · moderate
- Corroded or loose connector · easy
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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